It has been the practice to have an eyeglass lens ground to the prescription of an eye of a particular patient. The ground lenses were thereafter examined in a lensometer to determine if the lens was, in fact, properly ground to the specification involved. The lensometer was also used to determine the exact location of the optical center to which the eyeglass had been ground and to determine a line which would coincide with a horizontal line in the lens when mounted in the spectacles and which horizontal line would pass through the optical center of the lens. Three marks were placed on the glass, one to indicate the optical center and the other two to indicate the horizontal line. To obtain the geometric center of the lens, when cut to fit a particular frame of eyeglass spectacles, the horizontal difference between the optical center and the geometric center of the lens as mounted in a particular spectacle frame was determined from the prescription. Then a protractor or a millimeter scale was laid on the lens and another mark was made on the lens and it was attempted to place this last mark a precise number or parts of millimeters in accordance with the said difference. Due to human error and faulty equipment, errors were made. In my invention, the lens is held in the same position as it was held when the optical center of the lens was determined. A movable marker starting from the determined optical center is moved by means having micrometer adjustments an amount determined by the difference between the optical center of the lens and the geometric center of the lens when cut to a particular frame. This movable marker and its precise adjustable means eliminates error because of equipment and provides for equipment wherein human error is reduced to a minimum.